Higher derivatives of ERP responses to cross-modality processing.

Determining the links between cognitive processes and neuroelectrical brain activity (i.e., event-related potentials, ERPs) depends strongly on our understanding of how this activity fluctuates in response to stimuli; however, the way in which changes in ERP amplitudes can accelerate and decelerate over time has received only scant attention. The present study demonstrates that moment-to-moment changes (i.e., derivatives) of ERP responses convey information that is not readily accessible from the amplitude of response. Subjects exposed to visual and auditory stimuli either alone (unimodal) or combined (crossmodal) yielded different responses according to particular derivatives of ERP activation. In particular, an effect of cross-modality integration (stronger activation for crossmodal compared to unimodal stimuli) was detected in the higher derivatives of activation of a number of electrode sites spanning a fronto-centro-parietal distribution; in most sites, no such effect was detected in the amplitude of waveforms itself. These results suggest that information may be carried by the higher derivatives of ERP responses, and that distinct topographic distributions are associated with different derivatives of response. These different derivatives of response may in turn relate to different strategies for sensory processing in the brain, and in particular reflect a fundamental mode of information processing by time derivatives previously reported in cortex.